Gas turbine engines include a number of annular assemblies, such as shrouds, casings and nozzles, centred about the engine's axis, and defining annular passages for flow paths within the engine. These annular assemblies are typically formed by a series of circumferential segments. Seals are required between adjacent segments to avoid gas leakage between the segments across the annular assemblies. A poor seal will result in gas leakage from a high pressure side of the annular assembly to a low pressure side and lead to a reduction in engine efficiency.
It is known to use strip seals to form a seal between adjacent segments in these annular assemblies. Grooves are formed in each of the abutting faces of the segments so that the grooves are opposed to one another when the segments are assembled. A thin, typically metallic, strip is inserted into the grooves, opposite edges of the strip being received in respective grooves in the opposed faces of the segments, so the strip spans between the two segments to inhibit the flow of gas between the segments.
Often it is desirable to have strip seal portions that inhibit gas flow in an axial direction as well as a radial direction. To enable this, the opposed faces of adjacent segments will typically have an axially extending groove and a radially extending groove that intersect one another, into which the strip seal portions are received.
U.S. Pat. No. 4,524,980 describes a strip seal arrangement that can be accommodated in grooves that are angled to one another. In this arrangement, two straight strip seal sections are assembled to intersect with one another (to correspond to the intersection of the grooves they are to be mounted in) but this requires the strip sections to be formed with interlocking cut-outs, which adds to the complexity of the manufacture and assembly of the seal. U.S. Pat. No. 5,709,530 describes another example of interlocking strip seal sections.
U.S. Pat. No. 5,154,577 describes another strip seal arrangement that employs straight strip sections. In this arrangement, straight strip sections are received in respective ones of the radial and axial grooves but these strip sections terminate short of the intersection of the grooves. A third, bent corner strip section is used to provide the seal at the intersection of the grooves, extending around the corner at the intersection, with opposite ends of this short third strip overlapping ends of the other strips. Although this approach avoids the complexities of manufacturing interlocking strip segments, the need for a third strip section adds to the component count and the complexity of assembly of the strip seal arrangement.
In other known sealing arrangements, the junction of the axial and radial grooves is curved and a similarly curved, one-piece strip seal is received in the opposed grooves of adjacent segments to form the seal. However, such curved strip seals are difficult and expensive to manufacture to the desired tolerances and can be awkward to assemble.
U.S. Pat. No. 5,988,975 describes another form of one-piece strip seal in which the strip is bent and doubled back on itself to form upstanding portions that extend from a horizontal base portion of the strip. The upstanding portions are configured to lie in radial grooves in the adjacent components they span between, whilst the horizontal base of the strip is received in axial grooves in the components. This strip is complex to form and will be difficult to assemble into the grooves.